boost/interprocess/sync/scoped_lock.hpp

//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2005-2012. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////
//
// This interface is inspired by Howard Hinnant's lock proposal.
// http://home.twcny.rr.com/hinnant/cpp_extensions/threads_move.html
//
//////////////////////////////////////////////////////////////////////////////
#ifndef BOOST_INTERPROCESS_SCOPED_LOCK_HPP
#define BOOST_INTERPROCESS_SCOPED_LOCK_HPP
#if (defined _MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif
#include <boost/interprocess/detail/config_begin.hpp>
#include <boost/interprocess/detail/workaround.hpp>
#include <boost/interprocess/interprocess_fwd.hpp>
#include <boost/interprocess/sync/lock_options.hpp>
#include <boost/interprocess/exceptions.hpp>
#include <boost/interprocess/detail/mpl.hpp>
#include <boost/interprocess/detail/type_traits.hpp>
#include <boost/move/move.hpp>
#include <boost/interprocess/detail/posix_time_types_wrk.hpp>
//!\file
//!Describes the scoped_lock class.
namespace boost {
namespace interprocess {
//!scoped_lock is meant to carry out the tasks for locking, unlocking, try-locking
//!and timed-locking (recursive or not) for the Mutex. The Mutex need not supply all
//!of this functionality. If the client of scoped_lock<Mutex> does not use
//!functionality which the Mutex does not supply, no harm is done. Mutex ownership
//!transfer is supported through the syntax of move semantics. Ownership transfer
//!is allowed both by construction and assignment. The scoped_lock does not support
//!copy semantics. A compile time error results if copy construction or copy
//!assignment is attempted. Mutex ownership can also be moved from an
//!upgradable_lock and sharable_lock via constructor. In this role, scoped_lock
//!shares the same functionality as a write_lock.
template <class Mutex>
class scoped_lock
{
/// @cond
private:
typedef scoped_lock<Mutex> this_type;
BOOST_MOVABLE_BUT_NOT_COPYABLE(scoped_lock)
typedef bool this_type::*unspecified_bool_type;
/// @endcond
public:
typedef Mutex mutex_type;
//!Effects: Default constructs a scoped_lock.
//!Postconditions: owns() == false and mutex() == 0.
scoped_lock()
: mp_mutex(0), m_locked(false)
{}
//!Effects: m.lock().
//!Postconditions: owns() == true and mutex() == &m.
//!Notes: The constructor will take ownership of the mutex. If another thread
//! already owns the mutex, this thread will block until the mutex is released.
//! Whether or not this constructor handles recursive locking depends upon the mutex.
explicit scoped_lock(mutex_type& m)
: mp_mutex(&m), m_locked(false)
{ mp_mutex->lock(); m_locked = true; }
//!Postconditions: owns() == false, and mutex() == &m.
//!Notes: The constructor will not take ownership of the mutex. There is no effect
//! required on the referenced mutex.
scoped_lock(mutex_type& m, defer_lock_type)
: mp_mutex(&m), m_locked(false)
{}
//!Postconditions: owns() == true, and mutex() == &m.
//!Notes: The constructor will suppose that the mutex is already locked. There
//! is no effect required on the referenced mutex.
scoped_lock(mutex_type& m, accept_ownership_type)
: mp_mutex(&m), m_locked(true)
{}
//!Effects: m.try_lock().
//!Postconditions: mutex() == &m. owns() == the return value of the
//! m.try_lock() executed within the constructor.
//!Notes: The constructor will take ownership of the mutex if it can do
//! so without waiting. Whether or not this constructor handles recursive
//! locking depends upon the mutex. If the mutex_type does not support try_lock,
//! this constructor will fail at compile time if instantiated, but otherwise
//! have no effect.
scoped_lock(mutex_type& m, try_to_lock_type)
: mp_mutex(&m), m_locked(mp_mutex->try_lock())
{}
//!Effects: m.timed_lock(abs_time).
//!Postconditions: mutex() == &m. owns() == the return value of the
//! m.timed_lock(abs_time) executed within the constructor.
//!Notes: The constructor will take ownership of the mutex if it can do
//! it until abs_time is reached. Whether or not this constructor
//! handles recursive locking depends upon the mutex. If the mutex_type
//! does not support try_lock, this constructor will fail at compile
//! time if instantiated, but otherwise have no effect.
scoped_lock(mutex_type& m, const boost::posix_time::ptime& abs_time)
: mp_mutex(&m), m_locked(mp_mutex->timed_lock(abs_time))
{}
//!Postconditions: mutex() == the value scop.mutex() had before the
//! constructor executes. s1.mutex() == 0. owns() == the value of
//! scop.owns() before the constructor executes. scop.owns().
//!Notes: If the scop scoped_lock owns the mutex, ownership is moved
//! to thisscoped_lock with no blocking. If the scop scoped_lock does not
//! own the mutex, then neither will this scoped_lock. Only a moved
//! scoped_lock's will match this signature. An non-moved scoped_lock
//! can be moved with the expression: "boost::move(lock);". This
//! constructor does not alter the state of the mutex, only potentially
//! who owns it.
scoped_lock(BOOST_RV_REF(scoped_lock) scop)
: mp_mutex(0), m_locked(scop.owns())
{ mp_mutex = scop.release(); }
//!Effects: If upgr.owns() then calls unlock_upgradable_and_lock() on the
//! referenced mutex. upgr.release() is called.
//!Postconditions: mutex() == the value upgr.mutex() had before the construction.
//! upgr.mutex() == 0. owns() == upgr.owns() before the construction.
//! upgr.owns() == false after the construction.
//!Notes: If upgr is locked, this constructor will lock this scoped_lock while
//! unlocking upgr. If upgr is unlocked, then this scoped_lock will be
//! unlocked as well. Only a moved upgradable_lock's will match this
//! signature. An non-moved upgradable_lock can be moved with
//! the expression: "boost::move(lock);" This constructor may block if
//! other threads hold a sharable_lock on this mutex (sharable_lock's can
//! share ownership with an upgradable_lock).
template<class T>
explicit scoped_lock(BOOST_RV_REF(upgradable_lock<T>) upgr
, typename ipcdetail::enable_if< ipcdetail::is_same<T, Mutex> >::type * = 0)
: mp_mutex(0), m_locked(false)
{
upgradable_lock<mutex_type> &u_lock = upgr;
if(u_lock.owns()){
u_lock.mutex()->unlock_upgradable_and_lock();
m_locked = true;
}
mp_mutex = u_lock.release();
}
//!Effects: If upgr.owns() then calls try_unlock_upgradable_and_lock() on the
//!referenced mutex:
//! a)if try_unlock_upgradable_and_lock() returns true then mutex() obtains
//! the value from upgr.release() and owns() is set to true.
//! b)if try_unlock_upgradable_and_lock() returns false then upgr is
//! unaffected and this scoped_lock construction as the same effects as
//! a default construction.
//! c)Else upgr.owns() is false. mutex() obtains the value from upgr.release()
//! and owns() is set to false
//!Notes: This construction will not block. It will try to obtain mutex
//! ownership from upgr immediately, while changing the lock type from a
//! "read lock" to a "write lock". If the "read lock" isn't held in the
//! first place, the mutex merely changes type to an unlocked "write lock".
//! If the "read lock" is held, then mutex transfer occurs only if it can
//! do so in a non-blocking manner.
template<class T>
scoped_lock(BOOST_RV_REF(upgradable_lock<T>) upgr, try_to_lock_type
, typename ipcdetail::enable_if< ipcdetail::is_same<T, Mutex> >::type * = 0)
: mp_mutex(0), m_locked(false)
{
upgradable_lock<mutex_type> &u_lock = upgr;
if(u_lock.owns()){
if((m_locked = u_lock.mutex()->try_unlock_upgradable_and_lock()) == true){
mp_mutex = u_lock.release();
}
}
else{
u_lock.release();
}
}
//!Effects: If upgr.owns() then calls timed_unlock_upgradable_and_lock(abs_time)
//! on the referenced mutex:
//! a)if timed_unlock_upgradable_and_lock(abs_time) returns true then mutex()
//! obtains the value from upgr.release() and owns() is set to true.
//! b)if timed_unlock_upgradable_and_lock(abs_time) returns false then upgr
//! is unaffected and this scoped_lock construction as the same effects
//! as a default construction.
//! c)Else upgr.owns() is false. mutex() obtains the value from upgr.release()
//! and owns() is set to false
//!Notes: This construction will not block. It will try to obtain mutex ownership
//! from upgr immediately, while changing the lock type from a "read lock" to a
//! "write lock". If the "read lock" isn't held in the first place, the mutex
//! merely changes type to an unlocked "write lock". If the "read lock" is held,
//! then mutex transfer occurs only if it can do so in a non-blocking manner.
template<class T>
scoped_lock(BOOST_RV_REF(upgradable_lock<T>) upgr, boost::posix_time::ptime &abs_time
, typename ipcdetail::enable_if< ipcdetail::is_same<T, Mutex> >::type * = 0)
: mp_mutex(0), m_locked(false)
{
upgradable_lock<mutex_type> &u_lock = upgr;
if(u_lock.owns()){
if((m_locked = u_lock.mutex()->timed_unlock_upgradable_and_lock(abs_time)) == true){
mp_mutex = u_lock.release();
}
}
else{
u_lock.release();
}
}
//!Effects: If shar.owns() then calls try_unlock_sharable_and_lock() on the
//!referenced mutex.
//! a)if try_unlock_sharable_and_lock() returns true then mutex() obtains
//! the value from shar.release() and owns() is set to true.
//! b)if try_unlock_sharable_and_lock() returns false then shar is
//! unaffected and this scoped_lock construction has the same
//! effects as a default construction.
//! c)Else shar.owns() is false. mutex() obtains the value from
//! shar.release() and owns() is set to false
//!Notes: This construction will not block. It will try to obtain mutex
//! ownership from shar immediately, while changing the lock type from a
//! "read lock" to a "write lock". If the "read lock" isn't held in the
//! first place, the mutex merely changes type to an unlocked "write lock".
//! If the "read lock" is held, then mutex transfer occurs only if it can
//! do so in a non-blocking manner.
template<class T>
scoped_lock(BOOST_RV_REF(sharable_lock<T>) shar, try_to_lock_type
, typename ipcdetail::enable_if< ipcdetail::is_same<T, Mutex> >::type * = 0)
: mp_mutex(0), m_locked(false)
{
sharable_lock<mutex_type> &s_lock = shar;
if(s_lock.owns()){
if((m_locked = s_lock.mutex()->try_unlock_sharable_and_lock()) == true){
mp_mutex = s_lock.release();
}
}
else{
s_lock.release();
}
}
//!Effects: if (owns()) mp_mutex->unlock().
//!Notes: The destructor behavior ensures that the mutex lock is not leaked.*/
~scoped_lock()
{
try{ if(m_locked && mp_mutex) mp_mutex->unlock(); }
catch(...){}
}
//!Effects: If owns() before the call, then unlock() is called on mutex().
//! *this gets the state of scop and scop gets set to a default constructed state.
//!Notes: With a recursive mutex it is possible that both this and scop own
//! the same mutex before the assignment. In this case, this will own the
//! mutex after the assignment (and scop will not), but the mutex's lock
//! count will be decremented by one.
scoped_lock &operator=(BOOST_RV_REF(scoped_lock) scop)
{
if(this->owns())
this->unlock();
m_locked = scop.owns();
mp_mutex = scop.release();
return *this;
}
//!Effects: If mutex() == 0 or if already locked, throws a lock_exception()
//! exception. Calls lock() on the referenced mutex.
//!Postconditions: owns() == true.
//!Notes: The scoped_lock changes from a state of not owning the mutex, to
//! owning the mutex, blocking if necessary.
void lock()
{
if(!mp_mutex || m_locked)
throw lock_exception();
mp_mutex->lock();
m_locked = true;
}
//!Effects: If mutex() == 0 or if already locked, throws a lock_exception()
//! exception. Calls try_lock() on the referenced mutex.
//!Postconditions: owns() == the value returned from mutex()->try_lock().
//!Notes: The scoped_lock changes from a state of not owning the mutex, to
//! owning the mutex, but only if blocking was not required. If the
//! mutex_type does not support try_lock(), this function will fail at
//! compile time if instantiated, but otherwise have no effect.*/
bool try_lock()
{
if(!mp_mutex || m_locked)
throw lock_exception();
m_locked = mp_mutex->try_lock();
return m_locked;
}
//!Effects: If mutex() == 0 or if already locked, throws a lock_exception()
//! exception. Calls timed_lock(abs_time) on the referenced mutex.
//!Postconditions: owns() == the value returned from mutex()-> timed_lock(abs_time).
//!Notes: The scoped_lock changes from a state of not owning the mutex, to
//! owning the mutex, but only if it can obtain ownership by the specified
//! time. If the mutex_type does not support timed_lock (), this function
//! will fail at compile time if instantiated, but otherwise have no effect.*/
bool timed_lock(const boost::posix_time::ptime& abs_time)
{
if(!mp_mutex || m_locked)
throw lock_exception();
m_locked = mp_mutex->timed_lock(abs_time);
return m_locked;
}
//!Effects: If mutex() == 0 or if not locked, throws a lock_exception()
//! exception. Calls unlock() on the referenced mutex.
//!Postconditions: owns() == false.
//!Notes: The scoped_lock changes from a state of owning the mutex, to not
//! owning the mutex.*/
void unlock()
{
if(!mp_mutex || !m_locked)
throw lock_exception();
mp_mutex->unlock();
m_locked = false;
}
//!Effects: Returns true if this scoped_lock has acquired
//!the referenced mutex.
bool owns() const
{ return m_locked && mp_mutex; }
//!Conversion to bool.
//!Returns owns().
operator unspecified_bool_type() const
{ return m_locked? &this_type::m_locked : 0; }
//!Effects: Returns a pointer to the referenced mutex, or 0 if
//!there is no mutex to reference.
mutex_type* mutex() const
{ return mp_mutex; }
//!Effects: Returns a pointer to the referenced mutex, or 0 if there is no
//! mutex to reference.
//!Postconditions: mutex() == 0 and owns() == false.
mutex_type* release()
{
mutex_type *mut = mp_mutex;
mp_mutex = 0;
m_locked = false;
return mut;
}
//!Effects: Swaps state with moved lock.
//!Throws: Nothing.
void swap( scoped_lock<mutex_type> &other)
{
std::swap(mp_mutex, other.mp_mutex);
std::swap(m_locked, other.m_locked);
}
/// @cond
private:
mutex_type *mp_mutex;
bool m_locked;
/// @endcond
};
} // namespace interprocess
} // namespace boost
#include <boost/interprocess/detail/config_end.hpp>
#endif // BOOST_INTERPROCESS_SCOPED_LOCK_HPP